Derivative Financial Instruments (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Derivatives designated as hedging instruments
Derivative instruments gain (loss)
Derivative Instruments, Gain (Loss) Recognized in Income, Net	$ 8.4	$ 15.1	$ 25.8
Derivatives designated as hedging instruments | Interest income
Derivative instruments gain (loss)
Other comprehensive income to be reclassified to interest income within the next 12 months	0.1
Derivatives designated as hedging instruments | Fair Value Hedge | Interest Rate Swaps | Interest expense
Derivative instruments gain (loss)
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(8.2)	(14.1)	(17.3)
Derivatives designated as hedging instruments | Cash Flow Hedge | Interest income
Derivative instruments gain (loss)
Amount of gains and (losses) reclassified from AOCI to Income	0.2	1.0	8.5
Derivatives designated as hedging instruments | Cash Flow Hedge | Interest Rate Swaps | Interest income
Derivative instruments gain (loss)
Derivative Instruments, Gain (Loss) Recognized in Income, Net	0.2	1.0	8.5
Derivatives not designated as hedging instruments
Derivative instruments gain (loss)
Derivative Instruments, Gain (Loss) Recognized in Income, Net	25.5	23.1	20.8
Derivatives not designated as hedging instruments | Interest Rate Contracts | Other noninterest income
Derivative instruments gain (loss)
Derivative Instruments, Gain (Loss) Recognized in Income, Net	1.1	(1.1)	(0.4)
Derivatives not designated as hedging instruments | Option contracts | Other noninterest income
Derivative instruments gain (loss)
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(1.7)	0.1	(0.1)
Derivatives not designated as hedging instruments | Foreign Exchange Contracts | International services income
Derivative instruments gain (loss)
Derivative Instruments, Gain (Loss) Recognized in Income, Net	26.1	24.1	21.3
Derivatives designated and not designated as hedging instruments
Credit Risk Exposure and Collateral
Aggregate fair value of derivatives with credit-risk-related contingent features, net liability position	43.4
Collateral delivered on swap agreements, with credit-risk-related contingent features	30.7
Derivatives designated and not designated as hedging instruments | Interest Rate Swaps
Credit Risk Exposure and Collateral
Interest rate swap credit risk exposure	1.6	5.3
Collateral received from swap counterparties	1.0	5.0
Collateral delivered on swap agreements, without credit-risk contingent features	$ 18.0